We thought we'd carry on with our Christmas gift of knowledge. So far we have explored prices for turkey and Christmas trees, and this week we shall indulge ourselves with pudding. But before getting to our price forecasts for dried grapes, here's a brief cultural lesson.

There is a popular myth that plum pudding's association with Christmas goes back to a custom in medieval England stating that the "pudding should be made on the 25th Sunday after Trinity [and] be prepared with 13 (as a minimum) ingredients to represent Christ and the 12 apostles."

The perfect pudding should be dense, moist, and oozing with the decadence of rich fruits and brandy. A good pudding should take time, around 24 hours in total - as you need to marinate and rest it.

This year I will be purchasing the following:

1 lb dried mixed fruit (sultanas, raisins, currants)

1 oz mixed candied peel, finely chopped

1 small cooking apple (finely chopped)

4 tbsp brandy, plus a little extra for the chef

2 oz self-rising flour, sifted

1 level tsp ground mixed spice

1 1/2 tsp ground cinnamon

Grated zest and juice

½ large orange

½ lemon

4 oz shredded suet, beef or vegetarian

4 oz soft, dark brown sugar

4 oz white fresh bread crumbs

1 oz whole shelled almonds, roughly chopped

2 large, fresh eggs

As we can see, the most important part of any pudding, after the brandy, is the fruit.

Dried grapes or raisins and sultanas (golden raisins), are a global product, but California and Turkey are particularly important. The difference between raisins and sultanas comes down to the way the grapes are dried. Raisins are dried in the sun over three weeks, causing them to be a darker color as the sugar caramelises. Sultanas are dipped in a potash solution, meaning they can be dried in only ten days, making them lighter and sweeter. The US is the largest producer of raisins, and Turkey is the largest producer of sultanas.

California raisin prices have fallen during 2013 due to low demand but good production, with excellent yields reported from this year’s harvest. In contrast, dried grape production in Turkey has dropped sharply year-on-year to around 0.2m tons, after dry weather caused yields to fall. Because of this, the majority of the dried grape crop has been processed into sultanas rather than raisins, as sultanas are more important to the Turkish export market. This restricted supply, coupled with strong demand from Europe, has forced prices up in recent weeks.

So with prices higher for Turkish sultanas but lower for Californian raisins, it seems that I should opt for different quantities of dried fruits. However, it’s Christmas, so I shall follow the recipe and not worry about cost.